/*
    memvdp.c --
    Memory handlers for when the VDP reads the V-bus during DMA.
*/

#include "shared.h"

unsigned int vdp_dma_r(unsigned int address)
{
  switch((address >> 21) & 7)
  {
    case 0: /* Cartridge ROM */
    case 1: 
      return READ_WORD(cart_rom, address);

    case 2: /* Unused */
    case 3: 
      return 0xFF00;

    case 4: /* Work RAM */
    case 6:
    case 7:
      return READ_WORD(work_ram, address & 0xFFFF);

    case 5: /* Z80 area and I/O chip */

      /* Z80 area always returns $FFFF */
      if(address <= 0xA0FFFF)
      {
        /* Return $FFFF only when the Z80 isn't hogging the Z-bus.
           (e.g. Z80 isn't reset and 68000 has the bus) */
        return (zbusack == 0) ? 0xFFFF : READ_WORD(work_ram, address & 0xFFFF);
      }
      else
        /* The I/O chip and work RAM try to drive the data bus which
           results in both values being combined in random ways when read.
           We return the I/O chip values which seem to have precedence, */
        if(address <= 0xA1001F)
        {
          uint8 temp = gen_io_r((address >> 1) & 0x0F);
          return (temp << 8 | temp);
        }
        else
          /* All remaining locations access work RAM */
          return READ_WORD(work_ram, address & 0xFFFF);
    }

    return -1;
}

